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Re: [ESPResSo-users] error message about min_local_box_l

From: Axel Arnold
Subject: Re: [ESPResSo-users] error message about min_local_box_l
Date: Wed, 27 Nov 2013 12:02:47 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0

Also note that both nodes report this error, which means that it is not just one particle with excessive forces, so your system is really far of equilibrium. At a first glance the script looks ok, so you might want to check that your tabulated potential works as intended (i.e., read the forces from Espresso and compare to what you expect).


On 11/27/2013 07:40 AM, Olaf Lenz wrote:
It is hard to say when all we have is just the error message.
However, from the error message, it tells that something apparently created very large forces in the simulation and yielded a very high velocity. That can happen either when the time step is too large, or when particles overlap very much.
You said that you reduced the time step, but the error still occurred. How much did you reduce the time step? As a suggestion, start with making the time step really small, like 0.001 times the time step you had so far, and try again. If it works now, you can increase it again.
Another thing to look for is the initial forces. How did you set up the system? If you set up the system randomly, there is a good chance that some particles are very close to each other. Depending on the interaction potential that you use, this might result in very large forces. To get rid of these large initial forces, you can use a warm-up with force capping (inter forcecap) to get the system to a state where these large forces disappear.


2013/11/27 guozhicheng222 <address@hidden>
When I am running the DPD simulation I get the following error message:
Error in startup script: background_errors 0 {004 some particles moved more than min_local_box_l, reduce the time step} 1 <consent> 
    while executing
"integrate $int_steps"
    ("for" body line 5)
    invoked from within
"for {set i 0} { $i < $int_n_times } { incr i} {

    puts -nonewline "run $i at time=[setmd time] "

    integrate $int_steps
    if { $vmd_output=="y..."
    (file "run.tcl" line 95)
mpirun noticed that the job aborted, but has no info as to the process
that caused that situation.
Based on the error suggestion, I modified the time step smaller. However, it's not working. What's wrong with this? Thanks in advance for anyone's help.
Best regards!

Dr. rer. nat. Olaf Lenz
Institut für Computerphysik, Allmandring 3, D-70569 Stuttgart
Phone: +49-711-685-63607

JP Dr. Axel Arnold
ICP, Universität Stuttgart
Allmandring 3
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609

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